DE102010000582A1 - Linear motor with permanent magnetic latching - Google Patents

Abstract

A linear motor for optical systems, for example endoscopes, is described. The motor has a stator with a yoke element and two coils arranged side by side, which are energized in opposite directions. Furthermore, permanent magnets polarized in the same direction and in the axial direction are arranged on both sides of the coil pair. The rotor of the motor comprises a permanent magnet which is poled in opposite directions to the permanent magnets of the stator and is connected to a pole piece at each end. The pole pieces are arranged in such a way that each pole piece lies in the middle of one of the coils in the rest position. By applying current to the coil, the rotor can be moved in the longitudinal direction from a rest position.

Description

Technical area

The invention relates to a linear motor, in particular for optical systems. Such optical systems are used for example in endoscopes. In modern video endoscopes, a camera chip and an associated lens system are integrated into the endoscope tip. To set the focal length or the focus of the lens system, a miniaturized motor is needed.

State of the art

Classical endoscopes, as can be used, for example, for minimally invasive surgery, guide the image by means of rod lenses from the intracorporeal objective to the extracorporeal eyepiece. The rod lenses make the system rigid and limited in optical quality. Modern video endoscopes use a camera chip in the endoscope tip. Such an endoscope is in the US 7,365,768 B1 disclosed. This has a rigidly arranged lens in front of the camera chip. It is not possible to adjust the focal length of the lens.

The DE 196 18 355 C2 shows a linear drive which can be integrated in endoscopes for setting the focal length of a lens system. For this purpose, a permanent magnet is moved as a rotor within a stator coil. However, the linear drive is sluggish because of the large mass of the permanent magnet. The relationship between the coil current and the rotor position is not clear and makes an additional displacement sensor with position control necessary.

The DE 37 17 872 C2 discloses a drive with a rotor and a stator for a lens system in video cameras. The rotor consists of two iron sleeves, which are interconnected by a carrier for receiving the lens system. The stator has two coils and a single annular permanent magnet for generating the magnetic fields necessary for the movement between the coils. The complex structure of the drive can be well implemented in video cameras with lens diameters in the centimeter range, but is not scalable to the size required for endoscopic applications in the millimeter range.

In the DE 103 23 629 A1 discloses a traveling-field linear motor having at least three stator coils. By a phase-shifted energization of the coils, a traveling field is generated, which causes a displacement of the rotor with axial permanent magnets. To generate the traveling field, we require a complex drive circuit.

From the DE 10 2008 038 926 A1 a linear drive is known which has two axially polarized permanent magnets in the rotor. The rotor is powered by the current supply of the stator coils in axial. Direction deflected. In addition, the stable positions of the rotor are realized by the pole shoes mounted in the stator, so that a continuous displacement of the rotor is made possible in a cladding tube. The disadvantage here is the dependence of the stroke and the restoring forces of the soft magnetic stator pole pieces, whereby a high accuracy in the manufacture and assembly of these parts is required.

Presentation of the invention

The invention has for its object to provide a linear motor with such small dimensions that it can be used in endoscopes. Furthermore, the linear motor should have a defined zero point position and a reproducible deflection as a function of the drive signal. In addition, the linear motor should have large driving forces at low mass and thus allow fast, continuous and accurate positioning of the optical system in the largest possible range. The beam path through the optical system must not be blocked when moving the components. The power loss of the linear motor should be low, so that little heat is generated in the tip of an endoscope. For ease of manufacture and assembly, the drive should be composed of as few and geometrically simple individual components.

This object is achieved by a linear motor according to claim 1. Further developments of the linear motor are specified in the dependent claims.

The linear motor according to the invention comprises a stator and a linearly displaceable rotor. The stator has at least one coil and on the outside a return element, which is arranged at least substantially parallel to the direction of movement. Furthermore, at least one axially magnetized permanent magnet is provided on the stator. The rotor is at least partially enclosed by the at least one coil and has at least one permanent magnet and at least one pole piece. At rest, ie without energization, the linear motor, each pole piece is within a coil, preferably in the coil center. In the case of several juxtaposed coils of adjacent coils are each traversed in the opposite direction of current.

In a particularly advantageous embodiment of the invention, the stator comprises a first coil and arranged next to it a second coil. Both coils are traversed in the opposite direction of current ie energized. Furthermore, a first permanent magnet and next to the second coil, a second permanent magnet are arranged outside the two coils in addition to the first coil. The two permanent magnets are magnetized axially and in the same direction. The rotor has a first permanent magnet, which is magnetized in opposite directions to the permanent magnet of the stator. Furthermore, the first permanent magnet of the rotor is connected on both sides with a respective pole piece.

A further advantageous embodiment of this embodiment of the invention comprises an additional first pole piece in the stator. This is preferably arranged centrally between the two coils.

In a further advantageous embodiment of the invention, the stator has a first coil and arranged next to it a second coil. Both coils are opposite flows through the current. Between the first coil and the second coil, a permanent magnet is arranged. The rotor has a first permanent magnet, which is magnetized in opposite directions to the permanent magnet of the stator. Furthermore, the first permanent magnet of the rotor is connected on both sides with a respective pole piece.

In a further advantageous embodiment of this embodiment of the invention, the stator additionally has a first pole piece next to the first coil and a second pole piece adjacent to the second coil.

A further advantageous embodiment of the invention relates to a linear motor with a stator with a coil and arranged on both sides of the coil oppositely magnetized permanent magnet. The rotor also two mutually magnetized the permanent magnets, between which a pole piece is arranged. The magnetization of the permanent magnets of rotor and stator is also oriented in opposite directions, so that each north pole or south poles between rotor and stator are opposite.

Another embodiment of the invention relates to a linear motor with a stator with three coils, wherein the coils are each traversed alternately opposite current. If the middle coil flows through current in a first direction, the two laterally arranged from this coil with current flowing through in the opposite direction. On this side of this coil arrangement, a permanent magnet is arranged, wherein the two permanent magnets are magnetized opposite. The rotor has two permanent magnets, which are also magnetized opposite. The magnetization of the permanent magnets of rotor and stator is also oriented in opposite directions, so that each north pole or south poles between rotor and stator are opposite. Furthermore, a pole shoe is mounted between the two permanent magnets and also a respective pole shoe on the two free sides of the permanent magnets.

The various variants of the invention are preferably embodied mirror-symmetrically to a plane perpendicular to the central axis. This does not affect the magnetization directions of the permanent magnets. These are aligned according to their function. The mirror-symmetrical arrangement results in a symmetrical current-path characteristic and a stable zero point position of the rotor in the middle of the arrangement.

The length of the return element is longer than the length of the rotor. It is particularly advantageous if the length of the return element is greater than the length of the rotor plus the maximum travel of the rotor.

A linear motor according to the invention preferably has a rotationally symmetric rotor and / or a rotationally symmetrical stator. Preferably, the linear motor is designed rotationally symmetrical with annular yoke element, pole shoes, permanent magnets and an annular coil. The rotor and in particular the permanent magnets and the pole shoes are preferably hollow cylindrical, d. H. they have the form of a cylindrical sleeve. The beam path of an optical system can then pass through the sleeve. In particular, a lens or other optical element may be seated in the sleeve. Thus, the focal length and / or the focus of the optical system can be adjusted by a displacement of the sleeve.

The linear motor allows an exact adjustment of the position of the rotor relative to the stator between two end positions. In the linear motor, each coil current corresponds to a unique position of the rotor with respect to the stator. Thus, by adjusting the coil current of the rotor can be moved continuously in the travel range. As a result of this unambiguous association between the coil current and the rotor position, it is possible to dispense with the travel measurement necessary for determining the position of the rotor which is necessary according to the prior art. The individual components have a simple geometry (rings, sleeves) and are therefore easy to manufacture and assemble.

The pole shoes and the return element must always include ferromagnetic and / or soft magnetic materials.

The linear motor can be easily miniaturized up to a size of a few millimeters outside diameter. The travel distance between the two end positions of the rotor is typically about 1 to 3 mm for a motor with a few millimeters outside diameter.

The coil may optionally be wound on a bobbin or without bobbin. It can also be multi-part, d. H. consist of several windings.

A detailed description of the function of the engine can be found in the description of the figures.

In a further advantageous embodiment of the invention is between the stator and the rotor a sliding layer. This can be designed in particular in the case of a rotationally symmetrical arrangement as a sliding sleeve. In order to influence the magnetic fields as little as possible, the sliding layer should consist of a non-magnetic field-guiding material, in particular of a non-ferromagnetic material. Their surface preferably comprises a material having a low coefficient of friction, for example PTFE (polytetrafluoroethylene), silicon nitride, silicon carbide, polypara-xylylene polymers or DLC (diamond-like carbon), for example as described in US Pat US 5,478,650 disclosed.

The sliding layer can compensate for unevenness on the rotor-facing side of the stator.

The described linear motor can in an alternative embodiment with a flat, z. B. plate-shaped stator and also flat or plate-shaped pole pieces of the rotor can be realized. Alternatively, a plurality of linear motors arranged around a cylinder or a polygonal body may also be provided. For example, with a uniform arrangement of linear motors around a cylinder, stable guidance results.

A linear motor according to the invention can also consist of solid material and have at one end a plunger for the nanopositioning of instruments. Such a device is preferably used in molecular biology, microelectronics or neurosurgery.

It is particularly favorable if the coil ( 9 ) is supplied with a direct current with superimposed alternating current of small amplitude and a frequency up to 1 kHz. As a result, the static friction and the sliding friction can be reduced.

A further aspect of the invention is a method for operating a linear motor, wherein the linear motor is supplied with a direct current and a superimposed alternating current of small amplitude and a frequency up to a maximum of 1 kHz. As a result, the static friction or sliding friction inside the engine can be reduced.

Description of the drawings

The invention will now be described by way of example without limitation of the general inventive idea by means of embodiments with reference to the drawings.

1 schematically shows a linear motor according to the invention.

2 shows a variant of the linear motor with an additional pole piece in the stator.

3 shows a further variant of the linear motor with a permanent magnet between the coils.

4 shows a variant of the linear motor of Figure three, with additional pole pieces are arranged on the stator.

5 shows a further variant of the linear motor with only one coil.

6 shows a further variant of the invention with three coils.

7 shows the linear motor 1 with a lens.

8th shows the field curve in the linear motor with energized coil.

9 shows force-displacement characteristics of the linear motor with different coil currents

10 shows force-displacement characteristics of the linear motor with and without pole piece in the stator

1 schematically shows an embodiment of an inventive arrangement in a cylindrical design in section. The stator 1 includes a yoke element 10 in the form of a soft magnetic return tube, in the bore of a first coil 15 and a second coil 16 are arranged. On one side of the coils is a first permanent magnet 11 arranged. On the other side of the coils is a second permanent magnet 12 arranged. Both permanent magnets are axially in the same direction, that is magnetized in the same direction. A sliding layer 18 in the form of a sliding sleeve here closes the stator 9 inside and provides a low-friction surface for the runner. The sliding sleeve must be made of a non- ferromagnetic material. The runner 2 here includes a permanent magnet 21 and a first pole piece 23 on the side of the north pole of the permanent magnet and a second pole piece 24 on the side of the South Pole. The runner is oriented so that the north pole of the magnet 21 the north pole of the permanent magnet 11 in the stator opposite. Accordingly, then the south pole of the magnet 21 the south pole of the permanent magnet 12 in the stator opposite. This results in a repulsive reluctance force in both directions on the rotor and thus a stable center position in the middle between the two permanent magnets 11 . 12 of the stator. In the bore of the rotor, an element to be positioned, such as an optical component, can be introduced. The rotor is axially displaceable in both directions within the sliding sleeve. The central axis 3 is in rotationally symmetrical arrangements also the axis of rotation.

2 shows an example of a further variant of the invention. In the stator is between the first coil 15 and the second coil 16 a first pole piece 13 arranged.

3 shows a further variant of the invention. Here is only a single permanent magnet on the stator 11 intended. This one is between the first coil 15 and the second coil 16 arranged.

4 shows a further variant of the linear motor of Figure three. Here are additional pole shoes 13 . 14 laterally outside the coils 15 and 16 arranged.

In 5 Another variant of the linear motor is shown with only one coil. Here, the stator has only one coil 15 with two permanent magnets arranged laterally from the coil 11 . 12 on. The two permanent magnets 11 . 12 are magnetized oppositely in the axial direction. The runner has a first pole piece in the middle 23 on at the side in each case a first permanent magnet 21 and a second permanent magnet 22 are arranged. The two permanent magnets are also magnetized axially opposite. In this example, the two south poles of the permanent magnets are located 21 and 22 on the first pole piece 23 , The permanent magnets 11 Twelfth stator are magnetized axially opposite to the corresponding magnets of the rotor.

In 6 is disclosed a further variant of the invention with three coils. Here, the stator has a first coil 15 , a second coil 16 and a third coil 17 lying side by side. Laterally next to the coils are a first permanent magnet 11 and a second permanent magnet 12 arranged axially opposite magnetized. The runner has three pole shoes 23 . 24 and 25 , Between the first pole piece 23 and the second pole piece 24 is a first permanent magnet 21 arranged. A second permanent magnet 23 is located between the second pole piece 24 and the third pole piece 25 , The magnetization of the permanent magnets is as in the arrangement according to 5 , Due to the higher number of spools, the actuating forces can be increased and the positioning accuracy can be increased.

7 shows a linear motor 1 , with one more lens 5 represented by the linear motor in the direction of the central axis 15 can be moved.

8th shows a representation of the invention with the magnetic circuits in energized coils. There is a current here as indicated by the directional arrows, passed through the coils, leaving in the coil 15 in the upper half of the figure, the current flows into the plane of the drawing and accordingly flows out of the plane of the drawing in the lower half of the figure. The current flow through the coil 16 takes place in the opposite direction. The magnetic flux from the permanent magnet 21 over the two pole shoes 23 and 24 and the yoke element 10 penetrates the coils 15 and 16 , By a current flow through the coils is a Lorentz force in the direction of movement 4 generated on the runner. This acts on the reluctance force between the permanent magnet 21 of the rotor and the permanent magnets 11 . 12 of the stator.

9 shows the force-displacement curves for different coil currents. In the diagram, the force F on the rotor is shown as a function of the deflection z of the rotor. A positive force F is plotted up and a positive displacement z is plotted to the right. The curve 51 shows the force-displacement curve in the currentless coil, that is at a coil current zero. In the case of a positive deflection z of the rotor, that is to say in the z-direction to the right, the reluctance forces result in a negative restoring force F, which attempts to keep the rotor in its position. The restoring force is equal to zero in position P1. Thus, the rotor will assume a stable position at this point without energizing the coil. If the runner is forced out of this stable position in one of its two directions of movement as a result of externally acting forces, for example acceleration forces, then restoring forces act which force the runner back into the central position. The magnetic forces keep the rotor comparable to a mechanical spring in this position.

With a coil current in a first direction, the reluctance forces are superimposed with an additional Lorentz force. Thus, the curve shifts 51 in the direction of the curve 52 , This results in the point 22 which is in the positive z-direction of the Point 21 is removed, the restoring force is zero, so that the runner occupies a new stable position in this point. The same happens with an opposite polarity current, but in the opposite direction. It will be the turn 51 in the direction of the curve 53 postponed. The point P3 with the restoring force zero is now in the opposite direction of the original point 21 ,

The term coil current is used here. This is independent of the number of provided in the respective variant of the invention coils. Of course, adjacent coils are traversed by currents of opposite direction. When the polarity is reversed, the polarity of the currents thus also reverses through all the coils. The term amperage refers to the current through a coil.

10 shows the effect of a pole piece 13 . 14 in the stator based on force-displacement curves. The characteristics refer to de-energized coils. The illustration shows basically as in the previous figure, the function of the restoring force F on the rotor as a function of the deflection z. The curve 54 arises in a typical arrangement according to the invention. Will now be an additional pole piece 13 . 14 integrated into the stator, so there is a reduction of the restoring reluctance forces and thus a flatter characteristic. Thus, the characteristic can be adjusted within wide limits by the installation of additional pole shoes and of course by their dimensioning. An advantage of a flatter characteristic curve is, for example, that a lower coil current is required for actuating the rotor, which in turn leads to a lower power loss in the coils. Especially with endoscopic instruments, it is desirable to keep the power loss in the tip of the instrument as low as possible in order to influence the location of the examination as little as possible. Here, the use of an additional pole piece provides a simple optimization tool.

LIST OF REFERENCE NUMBERS

1

stator

2

runner

3

central axis

4

movement direction

5

lens

10

Ground element

11

First permanent magnet in the stator

12

Second permanent magnet in the stator

13

First pole piece in the stator

14

Second pole piece in the stator

15

First coil

16

Second coil

17

Third coil

18

Overlay

21

First permanent magnet in the rotor

22

Second permanent magnet in the rotor

23

First pole shoe in the runner

24

Second pole piece in the runner

25

Third pole shoe in the runner

31

First magnetic circle

41

First electromagnetic circuit

51

Force-displacement curve de-energized

52

Force-displacement curve with current in a first direction

53

Force-displacement curve with current in a second direction

54

Force-displacement curve without pole piece in the stator

55

Force-displacement characteristic with pole piece in the stator

F

Power on the runner

z

Deflection of the runner

P1

Position of the rotor in the de-energized state

P2

Position of the rotor with current in a first direction

P3

Position of the rotor with current in a second direction

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 7365768 B1 [0002]
• DE 19618355 C2 [0003]
• DE 3717872 C2 [0004]
• DE 10323629 A1 [0005]
• DE 102008038926 A1 [0006]
• US 5478650 [0024]

Claims (14)

Linear motor comprising a stator ( 1 ) with at least one coil ( 15 . 16 . 17 ) and at least one axially magnetized permanent magnet ( 21 . 22 ), which of a inference element ( 10 ) are enclosed, and one of the at least one coil enclosed, parallel to the stator slidable runner ( 2 ) with at least one axially magnetized permanent magnet ( 21 . 22 ) and one of the number of coils corresponding number of pole shoes ( 23 . 24 . 25 ), wherein without energization of the linear motor, each pole piece is located within a coil. Linear motor according to claim 1, characterized in that the stator ( 1 ) a first coil ( 15 ) and a second coil ( 16 ), wherein the first coil ( 15 ) in the opposite direction as the second coil ( 16 ) is energized, and that next to the first coil ( 15 ) a first permanent magnet ( 11 ) and next to the second coil ( 16 ) a second permanent magnet ( 12 ) is provided, wherein the two permanent magnets are magnetized in the same direction, and the rotor has a first permanent magnet ( 21 ) which is opposite to the permanent magnets ( 11 . 12 ) of the stator is magnetized and at each end with a pole piece ( 23 . 24 ) connected is. Linear motor according to claim 2, characterized in that the stator has a first pole piece ( 13 ) between the first coil ( 15 ) and the second coil ( 16 ) is arranged. Linear motor according to claim 1, characterized in that the stator ( 1 ) a first coil ( 15 ) and a second coil ( 16 ), wherein the first coil ( 15 ) in the opposite direction as the second coil ( 16 ) is energized, and that between the first coil ( 15 ) and next to the second coil ( 16 ) a first permanent magnet ( 11 ), and the rotor has a first permanent magnet ( 21 ), which in the same direction to the first permanent magnet ( 11 ) of the stator is magnetized and at each end with a pole piece ( 23 . 24 ) connected is. Linear motor according to claim 4, characterized in that the stator has a first pole piece ( 13 ) next to the first coil ( 15 ) and a second pole piece ( 14 ) next to the second coil ( 16 ) having. Linear motor according to claim 1, characterized in that the stator ( 1 ) a first coil ( 15 ) and that, in addition to the first coil ( 15 ) a first permanent magnet ( 11 ) and next to the second coil ( 16 ) a second permanent magnet ( 12 ) is provided, wherein the two permanent magnets are magnetized in opposite directions, and the rotor a first permanent magnet ( 21 ) on the side of the first permanent magnet ( 11 ) of the stator, which in opposite directions to the first permanent magnet ( 11 ) of the stator is magnetized and a second permanent magnet ( 22 ) on the side of the second permanent magnet ( 12 ) of the stator, in the opposite direction to the second permanent magnet ( 12 ) of the stator is magnetized, wherein between the first permanent magnet ( 21 ) of the rotor and the second permanent magnet ( 23 ) of the runner a first pole piece ( 23 ) is arranged. Linear motor according to claim 1, characterized in that the stator ( 1 ) a first coil ( 15 ), a second coil ( 16 ) as well as a third coil ( 17 ), wherein the first coil ( 15 ) in the same direction as the third coil ( 17 ) and both in the opposite direction as the second coil ( 16 ) and that next to the first coil ( 15 ) a first permanent magnet ( 11 ) and next to the third coil ( 17 ) a second permanent magnet ( 12 ) is provided, wherein the two permanent magnets are magnetized in opposite directions, and the rotor a first permanent magnet ( 21 ) on the side of the first permanent magnet ( 11 ) of the stator, which in opposite directions to the first permanent magnet ( 11 ) of the stator is magnetized and a second permanent magnet ( 22 ) on the side of the second permanent magnet ( 12 ) of the stator, in the opposite direction to the second permanent magnet ( 12 ) of the stator is magnetized, wherein on one side of the first permanent magnet ( 21 ) a first pole piece ( 23 ), between the first permanent magnet ( 21 ) of the rotor and the second permanent magnet ( 23 ) of the runner a second pole piece ( 24 ) and on one side of the second permanent magnet ( 22 ) a third pole piece ( 25 ) is arranged. Linear motor according to claim 1 or 2, characterized in that the length of the rotor ( 2 ) smaller than the length of the inference element ( 10 ). Linear motor according to one of the preceding claims, characterized in that in the interior of the rotor ( 2 ) an optical element ( 3 ) can be recorded. Linear motor according to one of the preceding claims, characterized in that the rotor is rotationally symmetrical. Linear motor according to one of the preceding claims, characterized in that the stator is rotationally symmetrical. Linear motor according to one of the preceding claims, characterized in that a sliding sleeve ( 6 ) with a material with a low coefficient of friction at the surface between the stator ( 1 ) and runners ( 2 ) is arranged. Linear motor according to one of the preceding claims, characterized in that the rotor ( 2 ) consists of solid material and has only one plunger for the nanopositioning of instruments. Method for operating a linear motor according to one of the preceding claims, characterized in that, in order to reduce the static friction and sliding friction, the direct current through the coil ( 9 ) a very small alternating current with frequencies up to 1 kHz is superimposed.

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